This invention relates to guidewires such as are commonly used in the placement of catheters at various locations in a patient's cardiovascular system. Typically, the guidewire is placed percutaneously into the blood vessel and a catheter having a lumen adapted to receive the guidewire is advanced over the guidewire. For example, the guidewire may be of the small diameter steerable type disclosed in U.S. Pat. No. 4,545,390 to Leary. The guidewire disclosed in the Leary patent is useful particularly in guiding small diameter catheters into distally located, small blood vessels such as the coronary arteries. The guidewire has a main wire with a tapered distal portion and a helical coil mounted to and about the tapered distal portion. The coil may extend distally beyond the distal tip of the tapered portion of the main wire and a safety wire may be provided to connect the distal tip of the main wire with the distal tip of the coil. The safety wire assures that if the distal portion of the spring breaks, it will remain attached to the guidewire so that the broken distal portion can be withdrawn from the patient.
In some instances, the safety wire presents some disadvantage in that it imparts additional stiffness to the distal tip of the guidewire. Additionally, the use of a separate safety wire tends to give the distal tip of the wire a directional characteristic, so that it will tend to bend more readily along a particular plane than in other directions. In some cases, the directional characteristic resulting from the use of the safety wire is undesirable in that it can be difficult to control the positioning of the tip. Therefore, it is desirable to provide a guidewire construction with a tip having less stiffness and in which the tip is equally flexible in all directions, while maintaining a safety connection between the main wire and the coil.
Another desirable feature is to provide a guidewire in which the distal end has a graduated stiffness transition so as to avoid kinking and possible trauma to the blood vessel.
Guidewires typically are advanced and placed in a patient's vascular system while monitoring the position of the guidewire fluoroscopically. It is desirable that the guidewire be sufficiently opaque to x-rays to provide a clear indication of the location and position of the guidewire but without obstructing the fluoroscopic image of the more proximally located portions of the blood vessel in which the guidewire is placed. Thus, there may be instances in which a greater radiopacity is preferred for the distal portion of the coil.
Another disadvantage which results from the use of a safety ribbon in the guidewire is that it results in relatively little strain relief in the event that the safety ribbon breaks, as may occur under a tensile load or when forming a curve in the distal end of the coil.
It is among the general objects of the invention to provide an improved guidewire construction which avoids the foregoing difficulties while providing the foregoing advantages.